Find the number of terms of the A.P. 7, 11, 15, ..., 139?

1.	Find the number of terms of the A.P. 7, 11, 15, ..., 139?
Answer» Here, a = 7 , d = 11 – 7 = 4 and l = 139 where l = a + (n – 1)d ⇒ 139 = 7 + (n – 1)(4) ⇒ 139 = 7 + 4n – 4 ⇒ 139 = 3 + 4n ⇒ 139 – 3 = 4n ⇒ 136 = 4n n = 136/4 = 34 Hence, the number of terms in the given AP is 34

Answer»

Here, a = 7 , d = 11 – 7 = 4 and l = 139

where l = a + (n – 1)d

⇒ 139 = 7 + (n – 1)(4)

⇒ 139 = 7 + 4n – 4

⇒ 139 = 3 + 4n

⇒ 139 – 3 = 4n

⇒ 136 = 4n

n = 136/4 = 34

Hence, the number of terms in the given AP is 34

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